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Oxidation of Metals

, Volume 47, Issue 3–4, pp 277–293 | Cite as

The role of microstructure on pesting during oxidation of MoSi2 and Mo(Si,Al)2 at 773 K

  • Katsuyuki Yanagihara
  • Kazimierz Przybylski
  • Toshio Maruyama
Article

Abstract

The pesting behavior of MoSi2 and Mo(Si,Al)2 has been examined in air at 773 K to clarify the origin and mechanism of pesting phenomena and the effect of aluminum on pesting phenomena. The initial cracks play a much more important role than the grain boundaries and the initial oxide layer in pesting. Mo and Si oxidize to amorphous Mo-Si-O simultaneously with about a 200% volume expansion. Therefore, large stress appears at the cracktips and induce many new cracks. MoO3 vaporizes from the Mo-Si-O layer on the external surface and crack surfaces causing the oxides in the initial cracks to become porous. Oxygen has a short-circuit path to enter the sample in the cracks. Therefore, the partial pressure of oxygen is sufficiently high to allow oxidation of Mo in the materials. The platelet-like MoO3 grows on the external surface and also in the cracks. Finally, the sample distintegrates into powder. Pesting of Mo(Si,Al)2 occurs in the same way, however, its rate is much lower than that of MoSi2. The role of Al is to decrease the initial crack density of the samples from the melt. Other effects of Al might be to decrease the oxygen flux toward the oxide-intermetallic interface and to increase the plasticity of the amorphous oxide being formed in the cracks.

Key words

MoSi2 Mo(Si,Al)2 pesting disintegration internal oxidation 

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Copyright information

© Plenum Publishing Corporation 1997

Authors and Affiliations

  • Katsuyuki Yanagihara
    • 1
  • Kazimierz Przybylski
    • 2
  • Toshio Maruyama
    • 1
  1. 1.Department of Metallurgical Engineering, Faculty of EngineeringTokyo Institute of TechnologyMeguro-ku, TokyoJapan
  2. 2.Department of Solid State Chemistry, Faculty of Materials Science and CeramicsUniversity of Mining and MetallurgyCracowPoland

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